﻿GEOLOGY. 
  41 
  

  

  Mr. 
  Boyer 
  says: 
  "The 
  deposit 
  consists 
  almost 
  entirely 
  of 
  C. 
  mar- 
  

   ginatus 
  and 
  C. 
  robustus 
  of 
  various 
  sizes 
  and 
  often 
  without 
  rims. 
  It 
  

   is 
  impossible, 
  in 
  certain 
  cases, 
  to 
  distinguish 
  between 
  these 
  two 
  

   forms. 
  The 
  variety 
  intermedia 
  is 
  between 
  the 
  two 
  and 
  was 
  created 
  

   by 
  Rattray." 
  

  

  The 
  second 
  slide 
  was 
  made 
  from 
  soft 
  shale 
  of 
  the 
  uppermost 
  por- 
  

   tion 
  of 
  the 
  Monterey, 
  from 
  the 
  Pinal 
  property 
  on 
  the 
  east 
  side 
  of 
  

   Pine 
  Canyon, 
  on 
  the 
  north 
  flank 
  of 
  Graciosa 
  Ridge. 
  The 
  following 
  

   diatoms 
  were 
  found: 
  

  

  Coscinodiscus 
  oculus 
  iridis 
  Ehrenberg 
  (abundant) 
  (PI. 
  XI, 
  fig. 
  XIX). 
  

  

  Coscinodiscus 
  marginatus 
  Ehrenberg. 
  

  

  Coscinodiscus 
  marginatus 
  var. 
  intermedia 
  Rattray. 
  

  

  Coscinodiscus 
  robustus 
  Grew 
  (PI. 
  XX, 
  fig. 
  4). 
  

  

  Coscinodiscus 
  radiatus 
  Ehrenberg. 
  

  

  Coscinodiscus 
  obscurus 
  A. 
  S. 
  (PL 
  XX, 
  fig. 
  2). 
  

  

  Coscinodiscus 
  nodulifer 
  Janisch. 
  

  

  Coscinodiscus 
  heteroporus 
  Ehrenberg. 
  

  

  Coscinodiscus 
  subtilis 
  Ehrenberg 
  (PI. 
  XX, 
  fig. 
  3). 
  

  

  Actinoptychus 
  undulatus 
  Ehrenberg 
  (rare) 
  (PL 
  XX, 
  fig. 
  la). 
  

  

  Arachnodiscus 
  ehrenbergii 
  var. 
  calif 
  ornica 
  (fragment). 
  

  

  Lithodesmium 
  cornigerum 
  Brun. 
  (PI. 
  XX, 
  fig. 
  1&). 
  

  

  According 
  to 
  Mr. 
  Boyer 
  this 
  second 
  sample 
  consists 
  chiefly 
  of 
  frag- 
  

   ments 
  of 
  Coscinodiscus 
  oculus 
  iridis 
  Ehrenberg, 
  which 
  is 
  a 
  larger 
  and 
  

   more 
  delicate 
  form 
  than 
  the 
  one 
  predominating 
  in 
  the 
  first, 
  and 
  

   both 
  he 
  and 
  Mr. 
  Keeley 
  comment 
  on 
  the 
  peculiar 
  absence 
  of 
  it 
  there. 
  

   The 
  difference 
  in 
  "the 
  fauna 
  in 
  these 
  different 
  localities 
  is 
  of 
  interest, 
  

   inasmuch 
  as 
  the 
  deposit 
  represented 
  by 
  the 
  first 
  slide 
  was 
  at 
  the 
  base 
  

   of 
  the 
  Monterey 
  and 
  that 
  represented 
  by 
  the 
  second 
  near 
  its 
  summit. 
  

  

  Besides 
  the 
  small 
  organisms 
  that 
  have 
  been 
  described 
  as 
  forming 
  

   a 
  portion 
  of 
  the 
  shale 
  material, 
  and 
  the 
  less 
  abundant 
  organic 
  remains 
  

   mentioned 
  on 
  pages 
  42-43, 
  the 
  deposits 
  of 
  Monterey 
  age 
  contain 
  

   a 
  considerable 
  percentage 
  of 
  fine 
  siliceous 
  and 
  aluminous 
  matter, 
  

   probably 
  of 
  detrital 
  origin, 
  in 
  the 
  shape 
  of 
  exceedingly 
  minute 
  clastic 
  

   grains. 
  The 
  chemical 
  analyses 
  of 
  specimens 
  from 
  different 
  localities 
  

   show 
  a 
  large 
  percentage 
  of 
  alumina, 
  the 
  presence 
  of 
  which 
  is 
  prob- 
  

   ably 
  the 
  result 
  of 
  fine 
  argillaceous 
  silt 
  settling 
  on 
  the 
  sea 
  bottom 
  

   to 
  aid 
  in 
  the 
  formation 
  of 
  the 
  shale. 
  The 
  origin 
  of 
  the 
  silica 
  is 
  more 
  

   in 
  doubt. 
  There 
  is 
  no 
  question 
  of 
  the 
  presence 
  of 
  a 
  large 
  amount 
  

   of 
  siliceous 
  diatom 
  skeleton 
  material, 
  and 
  the 
  many 
  fine-rounded 
  and 
  

   angular 
  particles 
  of 
  quartz 
  revealed 
  by 
  the 
  polarizing 
  microscope 
  in 
  

   the 
  unaltered 
  shale 
  indicate 
  that 
  the 
  sediments 
  derived 
  from 
  shore 
  

   areas 
  carried 
  quartz 
  grains 
  also, 
  but 
  there 
  is 
  no 
  proof 
  as 
  to 
  which 
  of 
  

   these 
  sources 
  supplied 
  the 
  bulk 
  of 
  the 
  silica, 
  of 
  which 
  the 
  shale 
  is 
  

   mostly 
  composed. 
  Besides 
  the 
  recognizable 
  diatom 
  remains 
  it 
  is 
  

   impossible 
  to 
  tell 
  how 
  much 
  of 
  the 
  shale 
  is 
  composed 
  of 
  similar 
  skele- 
  

   tons 
  that 
  have 
  been 
  crushed 
  beyond 
  any 
  semblance 
  of 
  their 
  original 
  

   form. 
  Comparatively 
  few 
  forms 
  are 
  perfectly 
  preserved, 
  most 
  of 
  

  

  